This invention relates to a method of automatically changing reels of strip material in packaging machines.
In particular, the present invention relates to a method especially adapted to be used on cigarette packaging machines, but advantageously capable of being used on any machine adapted for packaging or wrapping objects of relatively small dimensions, to permit the automatic changing of reels of wrapping material in strip form when said reels are exhausted.
The description which follows refers, without thereby in any way losing its generality, to packaging machines for cigarettes, for the reason that, as stated, the present invention finds its most advantageous application on this type of machine.
In general, modern packaging machines can be reduced schematically to a feed or conveying line, normally comprising one or more linear conveyors and a plurality of drum conveyors, along which the cigarettes issuing from a feed hopper and subdivided into groups are caused to advance in a continuous or step motion inside respective conveying chests.
Each group of cigarettes is subjected, in correspondence with precise points of the aforementioned line, to a series of wrapping operations, one or more of which are carried out by using strip wrapping material supplied from a reel.
With the objective of reducing dead working times to a minimum each feed reel is normally associated with a corresponding reserve reel, which should be capable of being substituted for the reel in use when the latter is close to being exhausted.
In general, the methods followed for the automatic replacement of a reel on cigarette packaging machines are two in number, and are distinguished from each other by the fact that the replacement of the reels is effected in one with the strip in motion, while in the other it is with the strip stopped. Leaving out the methods of automatic replacement with the strip in motion and examining solely the automatic methods with the strip stopped, it is possible to state that the latter generally provide for the use of a sensor adapted for emitting a signal when the reel in use is close to being exhausted. This signal generally determines the decoupling, for a determined period, of a transmission group interposed between an actuating motor and a group for entraining the strip becoming exhausted. This strip consequently undergoes a brief arresting sufficient for permitting it to be connected to one end of a strip of a new reel, and permitting it to be cut upstream of the junction zone in the direction of feed of the strip itself, with resultant unreeling of the new reel when the aforementioned transmission group is recoupled. The method of operation described above normally involves difficulties, for the reason that the recommencing of the feed of the strip of wrapping material should take place absolutely in phase with the feed of the said objects to be wrapped along said conveying line. Consequently, it is normally required that not only said transmission group shall be controlled by said end of reel sensor, but also that the transmission groups which control the feed of the conveying line shall be so controlled, with the undesired result of rendering the controlling system for same extremely complicated and expensive.